Return mechanism for a stopwatch or a chronograph

ABSTRACT

In a return mechanism of a chronograph or stopwatch, a plurality of heart-shaped cams are returned to zero position by means of a rotatable hammer having an equal number of acting surfaces which press against the cams during actuation. Each of the acting surfaces in excess of one is flexible with respect to the remainder of the hammer.

United States Patent Morita et al. [4 1 July 18, 1972 [54] RETURNMECHANISM FOR A [56] References Cited STOPWATCH OR A CHRONOGRAPH FOREIGNPATENTS OR APPLICATIONS [72] Inventors: Katsuhiko Morita- YoshloYamamoto both of-rokyojapn 466,152 1/1969 Sw tzerland ..58/74 285,8509/1952 Switzerland ..58/74 1 s Kabushlki Keisha Dflini Selkwha, Tokyo,286,565 10/1952 Switzerland ..ss/74 Japan [22] Filed: April 6, 1970Primary Examiner-Richard B. Wilkins [211 APPLNO': 25,718 AssistantExaminer-George H. Miller, Jr.

AttorneyBlum, Moscovltz, Friedman & Kaplan [30] Foreign ApplicationPriority Data 57] ABSTRACT April 16, 1969 Japan ..44/34l59 In a [6mmmechanism of a chrono graph or stopwatch, a plu- Apnl 7 vu l f ai l'ifiiii"?"8'21""1'74fl tality of heart-shaped cams are returned to zeroposition by 52 U.S Cl ..58/76 means "Mable hammer having an equal numberField of Search ..:.58/74-79 ing surfaces which press against the camsduring actuation. Each of the acting surfaces in excess of one isflexible with respect to the remainder of the hammer.

1 Claim, 3 Drawing Figures PATENTED JUU 8 I972 MQm $23553 STROKE RETURNMECHANISM FOR A STOPWATCH OR A CI-IRONOGRAPH DETAILS or THE INVENTIONThis invention relates to the improvement of a hammer being providedwith at least two acting surfaces and the improvement of characteristicsof the working stroke of the hammer. A hammer which works with at leasttwo hearts and a return hand is provided with the acting surfacescooperating with at least two hearts. In the return hand the actingsurfaces must contact the shoulder of the heart without a gap.

In an ordinary return mechanism, however, gaps cannot be avoided of allshoulders of heart except shoulders of one heart due to productionerror. The acting surfaces are adjusted by a file to reduce thegaps.Such adjustment has inconveniences which make the surfaces rough byfiling of acting surfaces and is apt to make the corner of the hammerround.

, Moreover, as the working force receives the feeble resistance at thebeginning of the push, the acting surfaces of the hammer acts with tooweak a force so that it cannot return the hand to zero and the heartstops.

The hammer according to this invention is provided with at least twoacting surfaces and at least two spring parts so as to absorb the gapdue to production error and to act without adjustment. By making thespring part of the hammer cooperate with the pin inserted in the plate,the working force at the beginning of the push is made stronger and theacting surface of the hammer acts on the heart and the handautomatically returns to zero.

EXPLANATION OF THE FIGURES FIG. I is a plane view of a return mechanismaccording to the invention;

FIG. 2 is a view and explanation of action; and

FIG. 3 is a characteristics diagram of the working stroke of a returnmechanism.

Referring now to the drawings, 1 is a hammer which is provided with, inthis case, two acting surfaces 1a and 1b which cooperate respectivelywith hearts 3 and 4. Hammer 1 has a spring portion 1d which gives thehammer the force of restitution. 6 is the locating pin which locates thehammer on restitution point. Usually the hammer is restored to theoriginal state as shown in FIG. 1. When returning the hand, the hammeracts in the state of action as shown in FIG. 2. The position of thehammer is settled by the rotating axle 2 and heart 3. The acting surfacela or 1b was hitherto filed and adjusted in order to reduce the gapbetween heart 4 and the acting surface lb. In this invention, the actingsurface lb and the hammer are combined by the spring portion 10, and thespring portion 11 is disposed to be automatically bent when la and heart3 make contact. In this way the gaps between more than two hearts andthe hammer l are absorbed without forcing the axle of heart 4. v

EXPLANATION OF THE WORKING FORCE When a pushed part 1f of the hammer isactuated externally the projection 1e of the spring portion 1d isconnected with a pin 5, and a strong working force is set in motion onthe acting surface 1b and makes the hearts 3 and 4 return automaticallyto zero. When the external pressure acts on the pushed part, and thehammer l rotates to some extent, the spring portion ld moves as shown inFIG. 2 in the direction of arrow A and the projection le slips out ofthe pin 5, thus weakening the working force of the acting surface. Therelation between working force of acting surface which acts on the heartand the stroke of the pushed part If is as shown in FIG. 3; the workingforce is strong at the beginning of the stroke and weak in the latterhalf. This working force therefore makes returning to zero more surethan a flat working force of an ordinary mechanism 6 as shown in FIG. 3.

The invention as above mentioned has the advantages of beingable toeliminate the. difficult adjustment without spoiling the finishing-10fthe acting surface. Moreover, as the spring portion of the ammer can bemoved, the workmg force Is strong at the beginning and weak in thelatter half, this mechanism can return hearts to zero automatically.

What is claimed is:

l. A return mechanism for a chronograph or a stopwatch, comprising ahammer-fulcrum, a hammer mounted rotatably on said hammer-fulcrum andhaving an integral hammer spring and two integral acting surfaces one ofwhich has flexibility with respect to the remainder of said hammer, twoessentially heart-shaped cams, each mounted rotatably on its owncam-fulcrum and disposed to coact with one of said acting surfaces whensaid return mechanism is actuated, said acting surfaces being atessentially equal distances from said hammer-fulcrum, and saidcam-fulcrums being at essentially equal distances from saidhammer-fulcrum, whereby the forces exerted by said acting surfacesagainst said cams during actuation will be essentially equal, and a pinso disposed as to press against said hammer spring and urge said hammeraway from said cams, the shape of said hammer-spring being such that theforce exerted by said spring is near maximum during the first portion ofsaid actuation, decreases during a further portion of said actuation andrises during the last portion of said actuation.

1. A return mechanism for a chronograph or a stopwatch, comprising ahammer-fulcrum, a hammer mounted rotatably on said hammer-fulcrum andhaving an integral hammer spring and two integral acting surfaces one ofwhich has flexibility with respect to the remainder of said hammer, twoessentially heartshaped cams, each mounted rotatably on its owncam-fulcrum and disposed to coact with one of said acting surfaces whensaid return mechanism is actuated, said acting surfaces being atessentially equal distances from said hammer-fulcrum, and saidcam-fulcrums being at essentially equal distances from saidhammer-fulcrum, whereby the forces exerted by said acting surfacesagainst said cams during actuation will be essentially equal, and a pinso disposed as to press against said hammer spring and urge said hammeraway from said cams, the shape of said hammer-spring being such that theforce exerted by said spring is near maximum during the first portion ofsaid actuation, decreases during a further portion of said actuation andrises during the last portion of said actuation.